Evaluation of vegetation and stream health within sites supported by the Hamilton City Council Plants for Gullies Programme

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Citation

Bylsma, R.J., Efford, J.T. & Kirby, C.L. (2013). Evaluation of the Hamilton City Council plants for Gullies programme. ERI report 015. Hamilton, New Zealand: Environmental Research Institute, The University of Waikato.

Abstract

Between August 2012 and March 2013, the Environmental Research Institute, University of Waikato, conducted a survey of randomly selected Hamilton gully sites which had received plants from the Hamilton City Council’s Plants for Gullies Programme. This survey assessed recent plantings, existing gully vegetation and stream health, along with property owner awareness and engagement with the key restoration principles.

The Plants for Gullies Programme has been extremely well received by the Hamilton community and gully owners. Survey participants were actively restoring their gully sites with the most common goal (c. 40%) being the establishment of native plant dominance within 10 years. Gully owners have a good understanding of restoration theory and practise; on average, plant placement in the gullies scored 15.7 out of 20 with consideration of plant environmental requirements and the concept of ecosourcing was understood by c. 76% of landowners surveyed. Also, most of the interviewed participants (c. 80%) were active in seeking guidance from other gullies, often through organised tours.

Current stream health was qualitatively assessed and characterised at each of the gully sites. Results provide baseline data for future monitoring. The majority of surveyed sites (c. 50%) had sand or silt substrate and the Bankwood gully had the best features for fauna habitat (e.g. debris and areas of low flow). At the time of visit, c. 60% of surveyed streams had clear water clarity. The poorest water clarity scores were in the Waitawhiriwhiri gully. When assessed on width, length and density, the average riparian buffer score was 12.8 out of 20 while the average stream shading score was 12.7 out of 20. The average bank stability score was 13.1 out of 20, reflecting an erosion problem that many gully owners talked about.

Surveyed gullies were diverse in terms of native and exotic vegetation structure and composition; native species contributed between c. 30% to 100% of surveyed trees and shrubs, whereas groundcovers were predominantly exotic. This assessment of gully sites has shown that the Plants for Gullies Programme improves native species diversity through the re-introduction of species that are not naturally regenerating. The Plants for Gullies programme is a powerful tool for engaging private landowners and making cost-effective change to Hamilton City’s native biodiversity. There is now a community of willing gully owners who will continue to restore their gullies with the support of a programme or network. It is our recommendation that the Plants for Gullies Programme is reinstated before this community loses momentum.